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Section 3 Floating-Point Unit (FPU)
Page 106 of 2108 R01UH0134EJ0400 Rev. 4.00
Sep 24, 2014
SH7262 Group, SH7264 Group
3.5 FPU Exceptions
3.5.1 FPU Exception Sources
FPU exceptions may occur on floating-point operation instruction and the exception sources are as
follows:
FPU error (E): When FPSCR.DN = 0 and a denormalized number is input (No error occurs in
the SH2A-FPU)
Invalid operation (V): In case of an invalid operation, such as NaN input
Division by zero (Z): Division with a zero divisor
Overflow (O): When the operation result overflows
Underflow (U): When the operation result underflows
Inexact exception (I): When overflow, underflow, or rounding occurs
The FPU exception cause field in FPSCR contains bits corresponding to all of above sources E, V,
Z, O, U, and I, and the FPU exception flag and enable fields in FPSCR contain bits corresponding
to sources V, Z, O, U, and I, but not E. Thus, FPU errors cannot be disabled.
When an FPU exception occurs, the corresponding bit in the FPU exception cause field is set to 1,
and 1 is added to the corresponding bit in the FPU exception flag field. When an FPU exception
does not occur, the corresponding bit in the FPU exception cause field is cleared to 0, but the
corresponding bit in the FPU exception flag field remains unchanged.
3.5.2 FPU Exception Handling
FPU exception handling is initiated in the following cases:
FPU error (E): FPSCR.DN = 0 and a denormalized number is input (No error occurs in the
SH2A-FPU)
Invalid operation (V): FPSCR.Enable.V = 1 and invalid operation
Division by zero (Z): FPSCR.Enable.Z = 1 and division with a zero divisor
Overflow (O): FPSCR.Enable.O = 1 and instruction with possibility of operation result
overflow
Underflow (U): FPSCR.Enable.U = 1 and instruction with possibility of operation result
underflow
Inexact exception (I): FPSCR.Enable.I = 1 and instruction with possibility of inexact operation
result